In a video and/or audio player presently in wide use, the information recorded on an information carrying medium such as a video and/or audio is read out by directing a laser beam at the surface of the disc through a suitable optical unit and scanning the record tracks on the surface of the disc with the laser beam. The beam reflected from or transmitted through the disc is processed to produce electric signals representative of the information read from the disc. In scanning the record tracks on the disc, the laser beam directed at the surface of the disc must be focussed correctly at target record tracks of the disc surface. The optical unit through which the laser beam is to be directed at the surface of the information carrying disc is thus driven for two-dimensional or three-dimensional oscillatory motions, viz., for oscillation in at least two directions perpendicular to each other with respect to the disc as the disc turns about the center axis thereof and/or the laser spot incident on the disc surface is moved toward or away from the center axis of the disc.
In order that the laser beam to scan the record tracks of the information carrying disc be correctly focussed on the surface of the disc, the objective lens which forms part of the optical unit must be at all times located at a predetermined distance from the surface of the disc throughout playback operation. Video and/or audio discs presently in use being subject to warpage although the degree of the warpage may differ from one disc to another, one of the important requirements of the electromechanical transducer assembly of a video and/or audio player is the capability to be responsive to the warpage of the disc as well known in the art. The optical unit of the electromechanical transducer assembly is for this reason required to be driven for slight movement in a direction parallel with the axis of rotation of the disc so as to be position adjusted toward or away from the surface of the disc during operation of the disc player.
Another important requirement of the electromechanical transducer assembly of a video and/or audio player is the capability to be responsive to the eccentricity of the circular or spiral record tracks of a video and/or audio and, thus, the objective lens provided in the optical unit of the electromechanical transducer assembly is further required to be driven for slight movement in a radial direction of the disc, viz., a direction perpendicular to the axis of rotation of the disc so as to be position adjusted toward or away from the axis of rotation of the disc during operation of the disc player.
The support structure used to support the optical unit of the electromechanical transducer assembly in the information pickup module of a video and/or audio player is for these reasons required to move, or oscillate, in at least two directions one parallel with and the other perpendicular to the axis of rotation of the disc in use.
One prior-art support structure of this nature is constructed to have two oscillatory systems adapted to permit the optical unit to oscillate in these two directions perpendicular to each other. The oscillating motion of the optical unit in one of these two directions is, however, inevitably accompanied by movement of the optical unit in the other direction. Such undesired movement of the optical unit results in errors in the oscillating motion of the unit in this latter direction. A problem is further encountered in that the coupled oscillation of the two oscillatory systems makes it difficult to control the oscillating motion of the optical unit in each of the two directions.
There is another type of support structure adapted to permit the optical unit to move, or oscillate, in at least two directions perpendicular to each other. This type of prior-art support structure uses two pairs of initially annular, elastic or viscoelastic spring elements provided under compression between support members which are movable with respect to each other, the optical unit being carried on one of the support members. The optical unit is elastically or viscoelastically positioned by the aid of these spring elements and is permitted to oscillate in the two directions with respect to the other of the support members by the elastic or viscoelastic deformation of the individual spring elements. The oscillating motions of the optical unit in the two directions thus result from the elastic or viscoelastic distorsion of the spring elements and tend to interfere with each other. This makes it extremely difficult to control the oscillating motion of the optical unit in each of the two directions. Where it is desired to have the springs designed to provide large amounts of displacement, each of the springs must have a large compliance constant, which will result in an increased tendency of the spring for torsional oscillation. The torsional oscillation of the spring in turn is another contribution to making it difficult to control the oscillating motion of the optical unit.
It is, accordingly, an important object of the present invention to provide an improved support structure for the optical unit of an electromechanical transducer assembly, the support structure being adapted to eliminate undesired movement of the optical unit in one direction when the optical unit is to be driven for movement in another direction.
It is another important object of the present invention to provide an improved support structure for the optical unit of an electromechanical transducer assembly, which support structure is useful for avoiding errors in the oscillating motion of the unit in each of the directions in which the optical unit is to be driven for movement.
It is still another important object of the present invention to provide an improved support structure for the optical unit of an electromechanical transducer assembly to avoid coupled oscillation of the oscillatory systems which form part of the support member.
It is still another important object of the present invention to provide an improved support structure for the optical unit of an electromechanical transducer assembly to make it easy to control the oscillating motion of the optical unit in each of the directions in which the optical unit is to be driven for movement.
Yet, it is still another important object of the present invention to provide an improved support structure for the optical unit of an electromechanical transducer assembly to reduce or eliminate the tendency for torsional oscillation of the spring elements forming part of the support structure and to further make it easy to control the oscillating motion of the optical unit.
While the support structure proposed by the present invention will be hereinafter described as being used with the electromechanical transducer which is included in the information pickup module of an optical information readout device, it should be borne in mind that a support structure according to the present invention is applicable to any type of electromechanical transducers involving two-dimensional motions or three-dimensional motions.